The invention is primarily designed for use with one or more fluorescent lamps because of their widespread popularity, but accommodates any type of lamp which requires an auxiliary power stabilizing circuit. In addition to fluorescents, commonly used alternative lighting of this type includes low voltage halogen lamps, and high intensity discharge (HID) lamps, both of which are more compact and efficient than incandescents. All of these lamps require a circuit device to condition the power, as they will not operate on the U.S. standard, 110 volts at 60 Hz. current. In this specification, the lamps will be described as "fluorescent", and the power stabilizing circuit as the "ballast", but it will be understood that the term "fluorescent" refers generically to any lamp which requires an on-board (or auxiliary) device or circuit to stabilize the current or the voltage, or both, and such circuit or device is covered by the term "ballast". The ballast converts the local power, whether it be AC, DC, 110-Volt, 277-Volt or whatever, to the form for which the lamp and system were designed, so the same lamp is used everywhere, with the electronics being the adaptive factor.
With the advantage of more efficiency, these lamps come with the baggage of the auxiliary circuit requirement, and an inherent circuit overheating problem. Heat damage will result from continued exposure to the hot cathodes of the lamp, especially if the circuit is enclosed in the same housing as the lamp. Although the subject lamps are more efficient than incandescents by a factor of up to eight or ten to one, nonetheless up to 75% of the energy they consume is dissipated as heat. And whereas manufacturers recommend that the ambient temperature be no higher than 40.degree. centigrade, and never greater than 50.degree., studies have shown that in a recessed ceiling can temperatures around the upper area where the ballast would be, routinely exceed 70.degree. centigrade in a 25.degree.-degree room using a 27-watt fluorescent. Higher wattages mean commensurately higher temperatures. In that temperature range, circuit life is halved for every 10.degree.-rise in temperature due to cumulative heat-induced insulation deterioration.
This disclosure specifically addresses ceiling-mounted fixtures, including "cans" recessed behind the the ceiling panels, and surface mounted fixtures similar in lighting function and external appearance to can mounts but not being recessed. Retrofitting these cans to accept fluorescent lighting, or other lighting which is more efficient than incandescent, presents several problems. For one thing, the compact fluorescent lamps and adapters which are designed to replace light bulbs are generally too long to fit within the can and extend out slightly beyond the housing in ceiling-mount installations with vertical lamps. The can's translucent diffusion covers may have to be removed, resulting in the creation of both glare and aesthetic problems, which present obstacles to upgrading hotel corridors, lobbies and rooms and other large commercial establishments whose multiplicity of can installations cry for conversion to low-energy lighting.
If the ceiling can is a side-mount version designed to use a horizontally extended incandescent bulb, the typical compact fluorescent adaptor and lamp designed for retrofitting will not fit at all, since the tube does not have the option of extending beyond the boundary of the can. There are cans designed specifically for housing fluorescent replacements, but making these installations as retrofit conversions is very labor intensive and expensive. Worse, when finished the ballasts are still at the hot end of the can, still subject to premature failure from continuous exposure to heat not only from the lamp but from hot pipes and other equipment that is found between the ceiling joists. Upgrading often cannot be economically justified by lower utility bills, even without considering the reduced lamp and ballast life expectancy.
Much of the heat problem is caused by the practice of using standard compact fluorescent adapters which have the ballast around the base. Heat is also generated by the ballast itself, although this heat is dwarfed by the heat output of the lamp. These base-mounted units work fine for floor and ceiling lamps where there is adequate ventilation and the lamp base housing the electronics is below, not above, the hot lamp. But an inverted can, even though provided with ventilation holes, accumulates heat to destructive levels. This problem is aggravated by the fact that electronic ballasts, which replace the older coiled wire transformer-type ballasts, are much more sensitive to heat than traditional ballasts. The newer design has advantages in efficiency, reduced volume and weight, and inherent packaging versatility stemming from the ability to separate the components into different areas of the mounting fixture for compactness. These advantages lead to the use of electronic ballasts in applications for which they are not suited.
It is probably relatively rare for a construction salesperson to advise the building owner, responsible for authorizing an upgrade, of these problems, which skewer the economic balance even more against replacement.
Due to these problems, although hotels and other commercial establishments are slowly converting to reduced power consumption lighting, still only a small fraction of the possible conversions are actually being made. With a clear cost disadvantage of upgrading in some installations, it is difficult for the establishment to justify to the shareholders the changeover as part of its duty as a world citizen. There is a need for a simple retrofit unit which will enable can-mounted lighting to take full advantage of the economics of fluorescent tubes by preventing premature burn-out of electronic ballasts.